Prepared statement, loop results to get more results - php

Question

I have a query where I'm taking several results from a single table. I then need to loop through each result to get information from other tables, however, I can't get it to work.
Here's my code:
<?php
$type = 1;
if ($stmt = $cxn->prepare('SELECT username FROM users WHERE type = ?')) {
$stmt->bind_param('i', $type);
$stmt->execute();
$stmt->bind_result($username);
while ($stmt->fetch()) {
if ($stmt = $cxn->prepare('SELECT count FROM posts WHERE username = ?')) {
$stmt->bind_param('s', $username);
$stmt->execute();
$stmt->bind_result($result2);
$stmt->close();
}
}
$stmt->close();
}
?>
I get an error:
Call to a member function fetch() on a non-object
How do I fix this?

Answer 1

I would highly recommend a native SQL JOIN for this because it will avoid unnecessary overhead in sending potentially thousands of queries:
SELECT
u.username,
p.count
FROM
users u
LEFT JOIN // processed as LEFT OUTER JOIN so the syntax is interchangeable just fyi
posts p
ON u.username = p.username
WHERE
p.type = ?
Explaining LEFT JOIN only, we'll keep it simple =)
In the SQL above we start with username from the users table as a whole
users u just grants us the shortcut syntax for u.username so that SQL is readable and doesn't fubar
Next we want to attach the posts p table where u.username = p.username because we need the p.count for each username
Lastly we filter this conglomerate of data based on p.type being equal to something
Please note that are many things at play here depending on the DBMS. Such things include query optimizers, the exact point of filtering, etc... but that is far outside the scope of simply getting the hang of what we are trying to achieve conceptually so I will not go into detail because it will only cause confusion.

Answer 2

You are overwritting your stmt variable. You should use another one, like
$type = 1;
if ($stmt = $cxn->prepare('SELECT username FROM users WHERE type = ?')) {
$stmt->bind_param('i', $type);
$stmt->execute();
$stmt->bind_result($username);
while ($stmt->fetch()) {
if ($stmtCnt = $cxn->prepare('SELECT count FROM posts WHERE username = ?')) {
$stmtCnt->bind_param('s', $username);
$stmtCnt->execute();
$stmtCnt->bind_result($result2);
$stmtCnt->close();
}
}
$stmt->close();
}